This invention relates to alignment of two elements of an apparatus, such as the primary and the secondary mirrors of a telescope and, more particularly, to the use of an array of detectors positioned about the secondary mirror, in conjunction with a corresponding array of reflective or diffractive optical elements positioned about the primary mirror, for redirecting light of a central source to the detectors by means of direct beams and crisscrossing beams to develop a measure of alignment including data as to deformation of the primary mirror.
In the construction of mechanical structures, it may be necessary to provide precise alignment of a first element of a structure to a second element of the structure. Accurate alignment can be accomplished best by use of optical apparatus. An important example of such a mechanical structure is a telescope wherein the first element corresponds to a primary mirror and the second element corresponds to a secondary mirror. In the usual construction of such telescopes, the two mirrors are positioned coaxially in spaced-apart relation, with a reflecting surface of the secondary mirror facing a reflective front side of the primary mirror.
In terms of an XYZ orthogonal coordinate system, wherein the Z axis coincides with the optical axis of the foregoing telescope, and the X and the Y coordinates are transverse to the Z axis, alignment concerns an offset between mechanical elements or mirrors in either the X direction or the Y direction, this being known as decentering. The alignment also concerns a displacement along the Z axis, known as despace, which alters a desired spacing between the two mechanical elements or mirrors. The alignment furthermore concerns rotation of the first mechanical element, or primary mirror, about either the X or the Y axis. In addition, particularly in the case of optical systems such as the foregoing telescope, there is concern as to any deformation or bowing of the primary mirror, particularly in the case of large mirrors of astronomical telescopes. Therefore, the alignment is concerned also with the detection of any bowing of the primary mirror, since the effects of this deformation on the performance of most in-situ alignment systems is significant.
A problem arises in that presently available optical systems for measurement of alignment present excessive difficulty in use and, furthermore, as in the case with a laser gauge system, require a succession of steps which, if interrupted, necessitates a restart of the calibration procedure.